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Re: 4.x -> 5.x locking?
On Wed, Nov 09, 2011 at 09:37:47AM -0500, Mouse wrote:
> >> membar_sync();
> >> mutex_exit(mtx);
> > mutex_enter and mutex_exit are implicit memory barriers (reads and
> > writes respectively are not allowed to be reordered).
> Oh! Thank you. Has that made it into mutex(9) in -current? If not, I
> offer my opinion that it should.
> Does mutex_exit also implicitly push writes to main RAM, or whatever
> else is necessary to make them visible to other CPUs? (A reordering
> barrier does not necessarily imply a global visibility barrier.)
I don't think it guarantees it by itself. That is, if you want to access
the data on a different CPU, you either need to take the mutex (and the
read barrier in mutex_enter) or issue an explicit barrier.
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